Abstract: :
Purpose: Kynurenic acid (KYNA), the tryptophan metabolite, endogenousNMDA antagonist is a putative endogenous neuroprotectant synthesizedin the eye along the kynurenine pathway. The purpose of thepresent study was to investigate the effect of excitatory aminoacids upon KYNA production in bovine retinal slices.Methods:Adult bovine retinas were chopped in slices and placed at culturewells. De novo KYNA production was investigated according tothe method of Turski et al. (1988). Quantitative analysis ofnewly synthesised KYNA was carried out using an HPLC systemand detected fluorimetrically according to the method of Shibata.Glutamate, aspartate and kainate were tested. Results: Glutamateat the concentration of 1, 0,1, 0,01 and 0,001 mM reduced KYNAsynthesis in the retinal slices to 23% (p<0,001), 35% (p<0,01),70% (p<0,05) and 88% (NS), respectively. The concentrationof glutamate reducing production of KYNA by 50% (IC50) was 0,035mM (0,02-0,06). Aspartate at the concentration of 1, 0,1, 0,01and 0,001 mM lowered KYNA synthesis in the retinal slices to43% (p<0,001), 57% (p<0,001), 80% (p<0,01) and 95%(NS), respectively. The IC50 for aspartate was 0,32 mM (0,18– 0,59). In contrast, kainic acid applied at the sameconcentrations turned out to be ineffective in diminishing KYNAsynthesis.Conclusions: These data demonstrate the inhibitingeffect of glutamate and aspartate on KYNA synthesis in bovineretinal slices.